The present invention relates to an improved means for retaining the side walls of a knocked down container in an upright position when the container is erected for use. In particular, the invention relates to an improved panel locking means applied to the corners of a knocked down container that is prepared from corrugated paperboard.
Folding cartons and trays having locking devices such as tabs and notches for securing the corners in the erected condition are known to those skilled in the art. Moreover, panel locking means comprising tabs and notches for corrugated paperboard are also known in the art. However, the known locking means for corrugated products have heretofore been limited to situations where only two panels are locked together, primarily because such locks have been found to be unsatisfactory for holding multiple thicknesses of heavy weight material.
Corrugated paperboard offers advantages over other packaging materials because of its great strength and durability. In particular, the vertical compression strength of corrugated paperboard is vastly superior to that of conventional paperboard packaging material. In addition, for those products which require a leak proof or moisture resistant container, corrugated paperboard can be treated with water impervious materials to satisfy such needs. Moreover, a web corner construction is particularly desireable for such products since web-type corners aid in making packages leak proof.
The known tab and notch locking schemes for corrugated materials have proven unsatisfactory for the following reasons. First, the existing tab designs tend to be weakened when folded into their mating notches particularly where the tab is creased to create a hinge connection. Secondly, the known notch configurations which have entry points that are equal to or larger than their base portions preclude the possibility of achieving a positive friction lock between the elements that can withstand the normal handling operations encountered by the container to which they are applied. Thus, the known panel locking schemes for corrugated materials are subject to premature failure, they generally do not provide sufficient holding power to maintain product integrity during normal handling, and are generally unsatisfactory for locking together multiple thicknesses of heavy weight corrugated material necessary to provide adequate strength.